TV on different aerial causing interference?
 

Bill Wright wrote:
"Jim" wrote in message
ronet...
charles wrote:
When some houses near my home were being re-roofed, the contractors
re-fitted aerials up to 6 to a mast, barely a foot apart.

Like this?

http://www.wrightsaerials.tv/roguesg.../061.html#img1

Bill
The aerials were all mounted vertically on a single mast, all with
vertical polarisation. In your example, the aerials are mounted on
horizontal spars and the vertical separation is greater. Which would be
worse for overlapping fields?

It's hard to say really, but in general I would have thought that if the
dipoles were broadside on there would be more chance of signal passing
from
one to the other.

Bill- Hide quoted text -

- Show quoted text -

Could be coupling between the two sections of coax running alongside
each other, this is likely to be comparable to the coupling between
the two antennas.

I believe many modern digital tuners use a zero IF technique with the
recovered I & Q signals being applied directly to the demodulator
chipset. So the avoidance of channels for fear of Local Oscillator re-
radiation problems imay no longer be necssary.




U&V are the un-weighted R-Y and B-Y in the case of the PAL system.
I&Q are near equivelents for NTSC.
In eather case you are going to need a Y signal as well.

--
Graham.

%Profound_observation%

TV on different aerial causing interference?
 

"Ian Jackson" wrote in message
...
In message , Woody
writes
"Ian Jackson" wrote in message
...
In message , Woody
writes
"Al" wrote in message
3.1.4...
Strange one this ...

Parents got a new TV for their kitchen recently (Samsung LE19R8) and
sure
enough their indoor aerial wasn't good enough as expected.

So, they had another aerial installed and a seperate downlead to the
kitchen. The aerials are both on the same chimney mast and the
downleads
run along side each other until they reach a lower level and go
their
seperate ways. (No, I don't know why they didn't get a booster and a
splitter).

2 TVs in the front room, one old analogue and an IDTV fed from one
aerial
with a passive splitter (yes, I know). There's a VCR in there
somewhere
also. Kitchen TV on it's own aerial.

Everything works fine ... Until the kitchen TV is put on ITV on
digital,
and then Channel 4 in the front room is unwatchable on analogue -
Snowy
vertical rolling. Fine on digital on the IDTV. Change channel on the
kitchen TV or go to ITV via analogue and everything is fine.

If I swap the kitchen TV and the analogue TV over there is no
problem.
It
sort of implies that there's something weird happening when the 2
digital
TVs are on different aerials.

I wanted to remove the VCR and the splitter and try some more
combinations
but the parents are paranoid that it won't work again (nice to be
trusted!).

I can't believe that the kitchen TV is putting interference up the
aerial
lead and that it's cross coupling with the other aerial. The coax
looks to
be good quality foil shielded and both aerials seem to be giving
good
signal strength.

I'm baffled :(

Al.



Likely that the local oscillator (or possibly the computer clock) is
getting back up the aerial and coupling across to the analogue aerial
or
downlead.

If you swap the TVs you said yourself that there is a VCR in there and
if the TV is the last item in the chain then there is no path back
through the VCR to the aerial - many VCR local outputs are amplified.

As others have said relocate one of the aerials, or if you have enough
signal fit an attenuator in the DTTV cable at the TV end. You will
then
maximise the interferring losses and possibly reduce it enough to
remove
the Ch4 problem.

For analogue channels, the 'N+5' and 'N=5' allocations were strictly
been abandoned? If so, I can see some muxes getting clobbered by an
analogue TV tuned to a channel five channels down.

But maybe they have still avoided this relationship? For example, I
see that, with the Crystal Palace allocation, no digital mux is N+5
wrt an analogue channel. However, there are three allocations where
there is something N+5 wrt a digital mux (25 on 30 analogue, 28 on 30
analogue, and 29 wrt 34 digital).

But do the digital STBs and TVs have the same local oscillator and IF
as analogue TVs - or do they use something different? If they are the
same, do the digital tuners simply have much less radiation of the
local oscillator?

Once again, correcting my mistake... Should be 28 on 33 analogue.

Emley (which I use) is analogue 37, 41, 44, 47, 51 and digital is 40,
43, 46, 49, 50, 52.

My simple maths suggests that the N+5/N=5 rule is truly no more.

You're dead right. A41 hits D46, and A47 hits D52. I'm surprised that this
does not cause the occasional problem. D46 also hits A51 but, assuming
that digital tuners are engineered to a much higher standard, and don't
radiate much local oscillator, that might be OK. Maybe the whole N+5/N-5
was a complete myth!
--
Ian

My guess is that it's not been a problem since we routinely
left the screening cans off the PC86 and PC88 valves so they
ran cooler!

--
Graham.

%Profound_observation%

TV on different aerial causing interference?
 

When this sort of problem occurs, a small one-in one-out amplifier,
followed by an attenuator if necessary, prevents anything getting back
up the downlead.

Digging up an old thread, but finally got back to the parents.

Tried a variable attenuator on it's own. No good. Too much signal loss.

Tried a cheap one-in two-out amp on it's own. Perfect. No need for any
attenuation as the 'new' TV seems quite happy with way too much signal
stuffed into it.

Result: Happy parents, cost to me 7 or 8 quid for the amp and a flylead.

Thanks for all of the input on this thread, it was really helpful and
educational :)

Al.

TV on different aerial causing interference?
 

Strange one this ...

Parents got a new TV for their kitchen recently (Samsung LE19R8) and
sure enough their indoor aerial wasn't good enough as expected.

So, they had another aerial installed and a seperate downlead to the
kitchen. The aerials are both on the same chimney mast and the
downleads run along side each other until they reach a lower level and
go their seperate ways. (No, I don't know why they didn't get a
booster and a splitter).

2 TVs in the front room, one old analogue and an IDTV fed from one
aerial with a passive splitter (yes, I know). There's a VCR in there
somewhere also. Kitchen TV on it's own aerial.

Everything works fine ... Until the kitchen TV is put on ITV on
digital, and then Channel 4 in the front room is unwatchable on
analogue - Snowy vertical rolling. Fine on digital on the IDTV. Change
channel on the kitchen TV or go to ITV via analogue and everything is
fine.

If I swap the kitchen TV and the analogue TV over there is no problem.
It sort of implies that there's something weird happening when the 2
digital TVs are on different aerials.

I wanted to remove the VCR and the splitter and try some more
combinations but the parents are paranoid that it won't work again
(nice to be trusted!).

I can't believe that the kitchen TV is putting interference up the
aerial lead and that it's cross coupling with the other aerial. The
coax looks to be good quality foil shielded and both aerials seem to
be giving good signal strength.

Replying to myself just to put this one to bed for anyone searching for
similar problems. Sorry about digging up an old thread!

Tried a variable attenuator on it's own. No good. Too much signal loss.

Tried a cheap one-in two-out amp on it's own. Perfect. No need for any
attenuation as the 'new' TV seems quite happy with way too much signal
stuffed into it.

Result: Happy parents, cost to me 7 or 8 quid for the amp and a flylead.

Thanks for all of the input on this thread, it was really helpful and
educational :)

Al.